1,291 research outputs found
Twin polaritons in semiconductor microcavities
The quantum correlations between the beams generated by polariton pair
scattering in a semiconductor microcavity above the parametric oscillation
threshold are computed analytically. The influence of various parameters like
the cavity-exciton detuning, the intensity mismatch between the signal and
idler beams and the amount of spurious noise is analyzed. We show that very
strong quantum correlations between the signal and idler polaritons can be
achieved. The quantum effects on the outgoing light fields are strongly reduced
due to the large mismatch in the coupling of the signal and idler polaritons to
the external photons
Strategies for protecting intellectual property when using CUDA applications on graphics processing units
Recent advances in the massively parallel computational abilities of graphical processing units (GPUs) have increased their use for general purpose computation, as companies look to take advantage of big data processing techniques. This has given rise to the potential for malicious software targeting GPUs, which is of interest to forensic investigators examining the operation of software. The ability to carry out reverse-engineering of software is of great importance within the security and forensics elds, particularly when investigating malicious software or carrying out forensic analysis following a successful security breach. Due to the complexity of the Nvidia CUDA (Compute Uni ed Device Architecture) framework, it is not clear how best to approach the reverse engineering of a piece of CUDA software. We carry out a review of the di erent binary output formats which may be encountered from the CUDA compiler, and their implications on reverse engineering. We then demonstrate the process of carrying out disassembly of an example CUDA application, to establish the various techniques available to forensic investigators carrying out black-box disassembly and reverse engineering of CUDA binaries. We show that the Nvidia compiler, using default settings, leaks useful information. Finally, we demonstrate techniques to better protect intellectual property in CUDA algorithm implementations from reverse engineering
Non-critically squeezed light via spontaneous rotational symmetry breaking
We theoretically address squeezed light generation through the spontaneous
breaking of the rotational invariance occuring in a type I degenerate optical
parametric oscillator (DOPO) pumped above threshold. We show that a DOPO with
spherical mirrors, in which the signal and idler fields correspond to first
order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape
of a Hermite-Gauss mode, within the linearized theory. This occurs at any
pumping level above threshold, hence the phenomenon is non-critical.
Imperfections of the rotational symmetry, due e.g. to cavity anisotropy, are
shown to have a small impact, hence the result is not singular.Comment: 4 pages, 1 figure, replaced with resubmitted versio
Orbital frustration at the origin of the magnetic behavior in LiNiO2
We report on the ESR, magnetization and magnetic susceptibility measurements
performed over a large temperature range, from 1.5 to 750 K, on high-quality
stoichiometric LiNiO2. We find that this compound displays two distinct
temperature regions where its magnetic behavior is anomalous. With the help of
a statistical model based on the Kugel'-Khomskii Hamiltonian, we show that
below T_of ~ 400 K, an orbitally-frustrated state characteristic of the
triangular lattice is established. This then gives a solution to the
long-standing controversial problem of the magnetic behavior in LiNiO2.Comment: 5 pages, 5 figures, RevTex, accepted in PR
Casimir torque between corrugated metallic plates
We consider two parallel corrugated plates and show that a Casimir torque
arises when the corrugation directions are not aligned. We follow the
scattering approach and calculate the Casimir energy up to second order in the
corrugation amplitudes, taking into account nonspecular reflections,
polarization mixing and the finite conductivity of the metals. We compare our
results with the proximity force approximation, which overestimates the torque
by a factor 2 when taking the conditions that optimize the effect. We argue
that the Casimir torque could be measured for separation distances as large as
1 Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding
The Meal Criterion Estimated in Grazing Dairy Cattle: Evaluation of Different Methods
The meal criterion (MC) has been found a useful tool to pre-treat intake behaviour data in dairy cows. It was defined as the longest interval between bouts that belong to the same meal (Tolkamp & Kyriazakis, 1999), necessary to cluster bouts to meals. The method of Yeates et al. (2001) calculating the loge-transformed intervals between bouts and using the Gaussian-Gaussian-Weibull (GGW) model to calculate the MC was found to provide the best estimation of the MC in biological as well as statistical terms. However, in grazing dairy cattle the MC-estimation has only been carried out by Rook & Huckle (1997) using a broken stick method. The aim of this study was to estimate the MC in grazing dairy cattle with the recently developed estimation methods
Molecular Gas Kinematics in Barred Spiral Galaxies
To quantify the effect that bar driven mass inflow can have on the evolution
of a galaxy requires an understanding of the dynamics of the inflowing gas. In
this paper we study the kinematics of the dense molecular gas in a set of seven
barred spiral galaxies to determine which dynamical effects dominate. The
kinematics are derived from observations of the CO J=(1-0) line made with the
Berkeley-Illinois-Maryland Association (BIMA) millimeter array. We compare the
observed kinematics to those predicted by ideal gas hydrodynamic and ballistic
cloud-based models of gas flow in a barred potential. The hydrodynamic model is
in good qualitative agreement with both the current observations of the dense
gas and previous observations of the kinematics of the ionized gas. The
observed kinematics indicate that the gas abruptly changes direction upon
entering the dust lanes to flow directly down the dust lanes along the leading
edge of the bar until the dust lanes approach the nuclear ring. Near the
location where the dust lanes intersect the nuclear ring, we see two velocity
components: a low velocity component, corresponding to gas on circular orbits,
and a higher velocity component, which can be attributed to the fraction of gas
flowing down the bar dust lane which sprays past the contact point toward the
other half of the bar. The ballistic cloud-based model of the ISM is not
consistent with the observed kinematics. The kinematics in the dust lanes
require large velocity gradients which cannot be reproduced by an ISM composed
of ballistic clouds with long mean-free-paths. Therefore, even the dense ISM
responds to hydrodynamic forces.Comment: To be published in the Astrophysical Journal, Nov. 20, 199
Thermal and dissipative effects in Casimir physics
We report on current efforts to detect the thermal and dissipative
contributions to the Casimir force. For the thermal component, two experiments
are in progress at Dartmouth and at the Institute Laue Langevin in Grenoble.
The first experiment will seek to detect the Casimir force at the largest
explorable distance using a cylinder-plane geometry which offers various
advantages with respect to both sphere-plane and parallel-plane geometries. In
the second experiment, the Casimir force in the parallel-plane configuration is
measured with a dedicated torsional balance, up to 10 micrometers. Parallelism
of large surfaces, critical in this configuration, is maintained through the
use of inclinometer technology already implemented at Grenoble for the study of
gravitationally bound states of ultracold neutrons, For the dissipative
component of the Casimir force, we discuss detection techniques based upon the
use of hyperfine spectroscopy of ultracold atoms and Rydberg atoms. Although
quite challenging, this triad of experimental efforts, if successful, will give
us a better knowledge of the interplay between quantum and thermal fluctuations
of the electromagnetic field and of the nature of dissipation induced by the
motion of objects in a quantum vacuum.Comment: Contribution to QFEXT'06, appeared in special issue of Journal of
Physics
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